Double acting draft control with sleeve



Jan. 10, 1967 F. PFISTER DOUBLE ACTING DRAFT CONTROL WITH SLEEVE FiledJan. 14, 1965 INVENTOR.

United States Patent 3,297,251 DOUBLE ACTING DRAFT CUNTROL WITH SLEEVELeo F. Pfister, Mendota, IlL, assignor to Conco Engineering Works, Inc.,a corporation of Illinois Filed Jan. 14, 1965, Ser. No. 425,393 7Claims. (Cl. 236-45) This invention relates to improvements in doubleacting barometric draft controls.

The use of double acting barometric draft controls in combustion systemsserves two purposes. The first is to regulate and maintain the draft ata substantially constant value such that the maximum efficiency of theunit may be maintained. With an excessive draft, the products ofcombustion ass through the heat exchange section of the combustion unitat a higher velocity than is desired because of the increased volume.When this occurs, the gases will not contact the heat exchanger surfacesfor a sufiiciently long period of time to allow maximum heat to beabsorbed from them, and fuel is wasted. Too little draft can cause poorcombustion so that excessive carbon monoxide is present in the productsof combustion. Free carbon or soot may also occur which will bedeposited on the walls of the heat exchanger of the device. Since sootis a poor conductor of heat, the accumulation of it upon the heatexchanger wall results in inefficient heat exchange and wasted fuel.

The other purpose of a double acting barometric draft control is torelieve downdrafts or overpressure in the stack that will affect theflame in the combustion unit. Commonly, such an overpressure will causepartial blockage or reversal of flow of the products of combustionWithin the stack. In a standard installation, the relieving of thepressure condition in the stack permits the spillage of the products ofcombustion into the room housing the combustion unit. While suchspillage may be tolerated for periods of short duration, it is apparentthat if this condition is prolonged, the atmosphere of the room housingthe combustion unit will be severely contaminated with the products ofcombustion. Such a result will inevitably lead to the choking of theflame of the combustion unit due to lack of oxygen and/or an unsafecondition for the operator of the combustion unit.

Accordingly, it has been good engineering practice to associate with thedouble acting barometric draft control, a cut-off mechanism, such as amercury switch in a time delay control circuit, for the burner that willbe actuated a predetermined time after the initiation of spillage of theproducts of combustion into the room housing the combustion unit. Suchmechanisms are customarily actuated by the movement of the control gateto a specified spillage position. It is therefore apparent that thesensitivity of the control in responding to a downdraft in the stackplays a great part in the actuation of the cut-off mechanism and thesafeness of the entire combustion system. It is further apparent thatthe sensitivity of the control is the major factor in determining therate of response of the control to a downdraft in the stack, and thus,the effect of the downdraft upon the flame in the combustion unit.

It is, therefore, the principal object of the invention to provide a newand improved double acting barometric draft control.

More specifically, it is an object of the invention to "ice provide adouble acting barometric draft control that is extremely sensitive tothe existence of a downdraft within the stack.

Another object of the invention is the provision of a double actingbarometric draft control having a housing and a gate pivotally mountedwithin the housing wherein the housing is provided with an extensionadja cent the gate such that at least a portion of the gate will swinginto an overlapping relation with the extension.

Another object of the invention is the provision of a double actingbarometric draft control including a housing having a gatepivotallymounted therein and an extension on the housing adjacent thegate wherein the distance from the gate in a closed position to the endof the extension is in the range of 25 to of the width of the housing.

Another object of the invention is the provision of a double actingbarometric draft control including a housing having a gate pivotallymounted therein, and an ex tension mounted on the housing adjacent thegate wherein the extension extends about at least 5% of the periphery ofthe housing.

Another object of the invention is the provision of a double actingbarometric draft control including a housing and a gate pivotallymounted therein, and a separate extension member attached to the housingadjacent the gate that is easily removable such that the sensitivity ofthe control may be adjusted in accordance with the requirements of anygiven application of use.

Other objects and advantages of the invention will become apparent fromthe following specification and drawings in which:

FIGURE 1 is a side elevation of a heating appliance having a fiue andstack and using a double acting barometric draft control made inaccordance with the invention;

FIGURE 2 is a view of a double acting barometric draft control accordingto the invention; and

FIGURE 3 is a sectional view of a double acting barometric draft controlmade in accordance with the invention taken along line 33 of FIGURE 2.

For purposes of illustration only, there is shown an embodiment of theinvention mounted on a double acting barometric draft control of thetype disclosed in US. Patent No. 2,819,024. It is to be understood,however, that the use of the invention is not limited to any specifictype of control such as that named above, but is readily adapted tovirtually every double acting barometric draft control.

A heating appliance of the fuel burning type is generally designated 10as shown in FIGURE 1. A vertically arranged flue 12 communicates withthe heating appliance 10 to receive the products of combustiontherefrom. A second fiue duct 14 channels the products of combustionfrom the flue 12 to a stack 16. Mounted on the flue 12 and communicatingtherewith is a double acting barometric draft control generallydesignated 18;

As seen in FIGURES 2 and 3, the control 18 comprises a generallycylindrical housing 20 having open ends 21 and 22, the first of which isadapted to be attached in a communicating relationship with the flue 12,and a pair of side openings 23 adjacent the end 22. The lower edges ofthe openings 23 serve to pivotally support a torque arm 24 having knifeedge bearings. A gate 26 of a size and shape such as to substantiallyclose the housing 20,

when it is in a position such as position A as seen in FIGURE 3, iseccentrically mounted on the torque arm 24. By virtue of the pivotalmounting of the torque arm 24, and thus the gate 26, the gate 26 mayassume a variety of positions within the housing in addition to theposition A wherein the control or major portion 27 of the gate 26 isoutwardly swung, such as in position B, orinwardly swung as in positionC, also shown in FIG- URE 3. It is to be noted, in normal operation,i.e., an updraft existing within the stack, the gate 26 will assume aposition such as the inwardly swung position C in FIGURE 3, or perhaps,if the proper draft is present in the stack 16 without admission ofextra draft gases by the control 18, closed position A will be assumed.On the other hand, if there is a downdraft within the stack 16 thatrequires relief, the gate 26 will assume an outwardly swung positionsuch as position B" in FIG- URE 3.

The torque arm 24 includes an offset portion 28 from which a link 30 issupported. The link 30 is attached to the torque arm portion 28 by meansof a pivotal connection 32. A yoke chain 34 is connected to the link 30and to the housing (not shown) and is adapted to support various weights(not shown) which apply a substantially constant bias to the torque arm24 in an updraft condition, and thus, normally maintain the gate 26 atan attitude that properly controls the draft in the stack. The weights(not shown) attached to the yoke chain 34 are suitably chosen inaccordance with the draft requirements of any given installation of aheating appliance.

On the side of the gate 26 opposite from the torque arm portion 28 is anadjustable counterweight 36 which is mounted on a threaded screw member38. The counterweight 36 is adjusted along the length of the screwmember 38 to substantially balance the weight of the major portion 27 ofthe gate 26 and the yoke chain 34 about the pivotal axis of the torquearm 24, but not the weight of the weights (not shown) supported by theyoke chain 34. Accordingly, the gate 26 will swing within the housingaccording to the dictates of the stack pressure and the restrainingtorques exerted on the torque arm 24 by the weights on the yoke chain34.

The structure thus far described is conventional, it being thatdisclosed in the aforementioned US. patent. While such prior art deviceshave served satisfactorily in many installations, their construction hasnot been endowed with the degree of sensitivity for downdraft controlachieved in a control made in accordance with the invention. To achievethe greater sensitivity contemplated by the invention, there is mountedon the open end 22 of the housing 20 an arcuate plate 40 which serves asan extension of at least a portion of the housing 20. The length of theextension plate 40 and the portion of the periphery of the housing 20about which the plate 40 extends can be varied within certain limitsdepending upon the degree of sensitivity required by any giveninstallation as will be seen hereinafter.

The connection between the extension 40 and the housing 20 may beachieved by conventional securing means such as screws 42 While it isnot critical, the use of releasable securing means, such as screws,permits ready interchangeability of various extension plates such that asupplier of the controls may stock a single control and a variety ofextension plates, any one of which may be selected to suit a giveninstallation. The extension plate 40 is placed on the housing 20 in sucha manner that the control or major portion 27 of the gate 26 will swingoutwardly into an overlapping relation with the extension plate 40,such'as is indicated by the outwardly swung downdraft position B of thegate 26 as seen in FIG- URE 3.

The following tables, the data for which was obtained on an eight inch,cylindrical double acting barometric draft control, illustrate theeffects of varying the length and peripheral extent about the housing ofthe extension plate.

TABLE I.EFFEOT OF EXTENSION LENGTH Distance between outer end of ex-Overpressure in Percent of housing tension and gate stack required toperiphery about in position A, swing gate 55 out which extension percentof width of wardly, inches W.O. plate extends housing 1 No extension.

TABLE I1.EFFECT OF PERIPHERAL EXTENT OF EXTENSION Overpressure inDistance between Percent of housing stack required to outer end ofperiphery about swing gate 55 extension and gate which extensionoutwardly, in position A, plate extends inches W.C. percent of width ofhousing 1 N 0 extension.

It is believed that the increased sensitivity and response to smalloverpressures or downdrafts in the stack found in a double actingbarometric draft control made in accordance with the invention is due toa directing action by the extension on the flue gases as the latter arespilled into the room housing the heating appliance. For example, if onewere to consider the control shown in FIGURE 3 without the extensionplate 40, it would be apparent that a greater percentage of the gasesbeing spilled could leave the control when the gate 26 is in a positionsuch as position B without exerting a force on the gate 26 than would bethe case with the extension present. In other words, the extension 40serves to confine the gases and direct them against the gate 26 when itis in an outwardly swung position, such as position B where the majorportion 27 of the gate 26 protrudes from the housing end 22. Thus, bydirecting a higher proportion of the flue gases being spilled againstthe gate, greater gate swing and control sensitivity will beaccomplished at the same stack overpressure.

Thus, it is believed apparent, that the invention does not rely on anyparticular housing shape or extension plate shape. Similarly, it will berecognized that the use of various means for controlling the inwardlyswung gate position during admittance of draft gases to the flue (suchas the gate position shown as C in FIGURE 3) does not substantiallyaffect the increased sensitivity and response to stack overpressureobtainable when an extension according to the invention is used with thedouble acting barometric draft control. It will be equally apparent, inview of the foregoing tables, that the various interrelations be-- tweenhousing width, extension length, and peripheral extent of the extensionabout the housing are factors of importance. Accordingly, it is believedobvious that a double acting barometric draft control constructed inaccordance with the invention is particularly well suited, although notlimited thereto, for use in installations having automatic burnercut-off means effective after prolonged spillage of flue gases caused byoverpressure within a stack because of the characteristic wherein asubstantial gate swing, sufficient for tripping a switch or the like toactuate the burner cut-off means, is produced by very low overpressures.

Having disclosed a specific embodiment of my invention as required by 35U.S.C. 112, I do not wish my invention to be limited to the constructionset forth, but rather, to be construed according to the true spiritthereof as set forth in the following claims.

I claim:

1. In a double acting barometric draft control including a cylindricalhousing having an end adapted to be attached to a flue; a gate includinga control portion and having a shape and size substantially conformingto the cross section of said housing such that said gate will close saidhousing in at least one position of said gate within said housing, andmeans pivotally mounting said gate within said housing for swingingmovement to either side of said one position; the improvementcomprising: an arcuate plate having an inner edge facing said end and anouter edge directed away from said end and mounted on the other end ofsaid housing and projecting outwardly therefrom to one side of said gatewhereby at least the control portion of said gate may swing into anoverlapping relation with said plate; said housing abutting said inneredge along the entire extent thereof; said plate extending about theportion of the periphery of said housing adjacent said control portionat least 120; the outer end of said plate being a distance of about6275% of the diameter of said housing from said gate when said gate isin said one position.

2. A double acting barometric draft control comprising: a cylindricalhousing having an end adapted to be attached to a fine; a gate includinga control portion and having a shape and size substantially conformingto the cross section of said housing such that said gate will close saidhousing in at least one position of said gate within said housing; meanspivotally mounting said gate within said housing for swinging movementto either side of said one position; and an arcuate extension on theother end of said housing and having an inner boundary embracing saidhousing along the entire peripheral extent of said extension, saidarcuate extension projecting outwardly therefrom and to one side of saidgate whereby at least the control portion of said gate may swing into anoverlapping relation With said extension; said extension extending aboutat least the portion of the periphery of said housing adjacent saidcontrol portion; the outer end of said extension being a distance ofabout 25-75% of the diameter of said housing from said gate when saidgate is in said one position.

3. The draft control of claim 2 wherein said extension comprises aseparate member attached to said housing.

4. In a double acting barometric draft control including a housinghaving an end adapted to be attached to a flue, a gate having a shapeand size substantially conforming to the cross section of said housingin at least one position of said gate within said housing, meanspivotally and eccentrically mounting said gate within said housing forswinging movement to either side of said one position, said gateincluding a major portion on one side of said pivotal mounting means anda minor portion on the other side of said pivotal mounting means, saidmajor portion being swingable away from said end and toward the otherend of said housing in response to a positive pressure in said flue andswingable toward said end in response to a negative pressure in saidflue; the improvement comprising: an outwardly directed extension onsaid other end of said housing along the periphery thereof adjacent saidmajor portion and to one side of said gate whereby said major portionmay swing into an overlapping relation with said extension, the innerboundary of said extension forming a substantially continuous surfacewith said housing.

5. The draft control of claim 4- wherein said extension comprises aseparate member attached to said housing.

6. The draft control of claim 4 wherein said extension extends beyondsaid gate in said one position a distance in the range of about 2575% ofthe width of said housing.

7. The draft control of claim 4 wherein said extension extends about atleast 5% of the periphery of said housing.

References Cited by the Examiner UNITED STATES PATENTS 2,818,216 12/1957Field 23645 FOREIGN PATENTS 638,922 12/1952 Great Britain.

ALDEN D. STEWART, Primary Examiner.

1. IN A DOUBLE ACTING BAROMETRIC DRAFT CONTROL INCLUDING A CYLINDRICAL HOUSING HAVING AN END ADAPTED TO BE ATTACHED TO A FLUE; A GATE INCLUDING A CONTROL PORTION AND HAVING A SHAPE AND SIZE SUBSTANTIALLY CONFORMING TO THE CROSS SECTION OF SAID HOUSING SUCH THAT SAID GATE WILL CLOSE SAID HOUSING IN AT LEAST ONE POSITION OF SAID GATE WITHIN SAID HOUSING, AND MEANS PIVOTALLY MOUNTING SAID GATE WITHIN SAID HOUSING FOR SWINGING MOVEMENT TO EITHER SIDE OF SAID ONE POSITION; THE IMPROVEMENT COMPRISING: AN ARCUATE PLATE HAVING AN INNER EDGE FACING SAID END AND AN OUTER EDGE DIRECTED AWAY FROM SAID END AND MOUNTED ON THE OTHER END OF SAID HOUSING AND PROJECTING OUTWARDLY THEREFROM TO ONE SIDE OF SAID GATE WHEREBY AT LEAST THE CONTROL PORTION OF SAID GATE MAY SWING INTO AN OVERLAPPING RELATION WITH SAID PLATE; SAID HOUSING ABUTTING SAID INNER EDGE ALONG THE ENTIRE EXTENT THEREOF; SAID PLATE EXTENDING ABOUT THE PORTION OF THE PERIPHERY OF SAID HOUSING ADJACENT SAID CONTROL PORTION AT LEAST 120*; THE OUTER END OF SAID PLATE BEING A DISTANCE OF ABOUT 62-75% OF THE DIAMETER OF SAID HOUSING FROM SAID GATE WHEN SAID GATE IS IN SAID ONE POSITION. 